dag: Dagger core loop

[abstraking]

We need a loop that on round N:

• Creates a new block
• Takes Messages/Blocks from round N-1
• Packs links/hashes of messages/blocks from round N-1
• Takes all Batches out of BatchPool
  • Must only be locally produced Batches
• Puts Batches' hashes in the Block
• Broadcasts the block
• Deletes batches in the broadcasted block from the pool.